Development of soil rotational rheometer and experiment on plastic flow characteristics of conditioned soil in earth pressure balance shield

A soil rotational rheometer is developed for investigating plastic flow characteristics of conditioned soil in the bulk chamber and the screw conveyor of earth pressure balance shield (EPBS). The device belongs to variable pressure and controlled strain rate rotational rheometer. It is capable of obtaining apparent viscosity by measuring the torsional shear applied to a standard vane with controlled pressure and strain rate. The test sands come from a section of a metro and are prepared by the same conditioning treatments under different initial moisture contents (5%, 10% and 15%). The test conditions contain four confining pressure levels (100, 200, 300 and 400 kPa) and seven vane speeds (1/3.4, 1/4.1, 1/5, 1/6.4, 1/9, 1/15 and 1/30 RPM). The results show that the relationship between shear stress and stain rate of foam conditioned sand fits the Bingham fluid model. It belongs to the visco-plastic non-Newtonian fluid. The viscosity coefficient and the yield stress increase with the increase of the confining pressure. The device is a valuable tool for comparing plastic flow characteristics of conditioned soil in EPBS and the test support for investigating distribution of pressure for simulation of soil flow in the working chamber and along the screw conveyor and developing pressure balance control in EPBS.